Caffeine, a methylxanthine and the most widely used psychotropic drug in our society, is a potent central nervous system (CNS) stimulant. The effects of caffeine on cognitive efficiency in old people have not been performed. In the young, caffeine often has a beneficial effect on those cognitive processes which tend to decline in the elderly, but it is not clear whether the drug has the same effect on cognition in the old. The objective of the proposed research is to provide information on the acute effects of caffeine on specific cognitive processes (memory, attention, language comprehension, spatial ability and reaction time) in relation to age and cognitive dysfunction. Healthy old people with mild demential (probable Alzheimer's disease by physician diagnosis), healthy age-matched controls and healthy young controls will be studied. Since cognitive dysfunction is a problem in advancing age and a major problem in Alzheimer's disease, it is hoped that data generated in this study will contribute to an effort to identify commonly used drugs which may favorably alter cognitive processes in the aged. A double-blind ramdomized cross over protocol will be used to study the effects of a single dose of caffeine (250 mg) on specific cognitive processes. Twenty-four subjects will be studied (8 young normal, 8 old normal, 8 Alzheimer's patients). Blood samples will be obtained for assay of plasma levels by high pressure liquid chromatography. The Nowliss Mood Adjective check list will be administered after each blood sample. The cognitive tasks have been selected to measure specific cognitive abilities. Computerized stimulus presentation and response recording will be employed. The immediate goal of this small pilot project is to obtain statistical data which will permit estimation of sample sizes for a larger, more definitive study and to determine the need for related studies to examine dose-response relationships, chronic vs. acute effects, comparative effects of various methylxanthines (caffeine, theophylline, theobromine) and the role of circadian rhythms on the cognitive effects of methylxanthines.